Pressurized reservoir for cavitationfree supply to pump



1957 R. H. SULLWOLD ETAL 2,809,596

PRESSURIZED RESERVOIR FOR CAVITATION-FREE SUPPLY TO PUMP Filed June 9,1954 f I0 T L.- as 28 1 \\\\\\\\\\\;\l\\\\\\\\\ 5.

Richard H. Sullwold a 7 Louis E. Berfhelson INVENTORS AT TORNE Y.

PRESSURIZED RESERVOIR FOR CAVITATION- FREE SUPPLY TO PUMP ApplicationJune 9, 1954, Serial N 0. 435,569

4 Claims. (Cl. 103-223) The present invention relates generally tohydraulic pressure systems and pumping means therefore, and moreparticularly to improvements in such systems whereby cavitation andsimilar conditions are prevented and eliminated.

In many hydraulic pressure systems, wherein rotary pump means are usedfor developing suitable actuating pressures, as in aircraft hydraulicsystems, conditions in the suction line to the pump frequently give riseto cavitation and similar problems. As i well known, cavitation isinherently an unstable phenomenon and may arise through the lowering ofthe fluid pressure and the formation of vapor bubbles in a liquid. Whensuch cavities of air and vapor form, the flow conditions are changed tothe detriment of the efficiency of the pumping means and that of thehydraulic system. Cavitation is also undesirable inasmuch as it createspressure waves which are frequently repeated at high frequencies andproduce impacts of such itensities that portions of the pump and theadjacent system components may be seriously damaged.

It is known that numerous prior elforts have been made to prevent orminimize cavitation within fluid systems by increasing the suction headto the pump, pressurizing the liquid reservoir or storage container byvarious means so as to maintain the suction line to the pump undersufficient pressure. The present invention is an improvement upon suchsystems in that a pressure fluid line is branched off from the highpressure pump discharge to a relatively small diameter piston andcylinder unit mounted upon the wall of the fluid reservoir in suchmanner as to apply a continuous force upon a floating piston in thereservoir for maintaining the stored fluid under pressure. Theimprovement resides essentially in a combined liquid storage reservoirto which the pressurizing piston and cylinder is mounted and suitablylinked to the floating piston there is an indicating means for showingthe amount of liquid within the reservoir at all times. The presentinvention also resides in the cavitation-free hydraulic system as wellas in the details and general arrangement of the improved storage andpressurizin components.

it is, accordingly, a major objective of the present invention toprovide an improved hydraulic pressure system in which cavitation of thepump means and adjacent conduits is substantially eliminated. It is afurther object to provide an improved liquid storage reservoir withmeans for its automatic pressurization by the pump means within thesystem. It is a further object to provide an improved pressurized liquidreservoir of relatively li ht weight, which is positive-acting andfoolproof in its operation. A further object resides in providing such apressurized reservoir which is automatically pressurized by operation ofthe pump thereby insuring pressure upon the stored liquid Whenever thepump is operating. A still further object resides in the provision ofsuch a pressurized reservoir of the airless piston type tates Patent 6"ice with means for indicating the amount of liquid stored within thecontainer.

Other objects and advantages of the present invention will occur tothose skilled in the art after the reading of the following description,taken in conjunction with the accompanying drawings, forming a parthereof, in which:

Fig. l is a diagrammatic view of a hydraulic pressure actuating systemto which an improved form of the pressurized reservoir has been applied;and

Fig. 2 is an enlarged cross-sectional view of the pressurized reservoirshown in Fig. 1.

Referring to Fig. l, the hydraulic pressure system includes the rotarypump 5 discharging into the high pressure line 6 from which a branch 7is connected to the pressurizing auxiliary cylinder 8. The maindischarge line 6 from the pump 5 extends through the pressure reliefvalve 9 and continues through to the main pressure line 11, the reliefline 12 from the valve 9 being connected to the main return line 13 forreturn of fluid to the main fluid reservoir 10. An indicator 15, to bemore fully described below, shows the quantity of fluid in the reservoirat all times. In addition to the return line connection 13 to the bottomof the reservoir 10 it is provided with an outlet for the suction line14 to the pump 5 and a further line 16 to the pressure relief valve 17from whence, in the case of an aircraft installation, for example, therelieved liquid may be discharged into a suitable sump provided for suchpurposes or otherwise passed overboard.

The main pressure line 11 may continue to the fourway rotary selectorvalve 18 provided with the operating handle 19 for selective connectionof the pressure and return lines 11 and 13, respectively, to either ofthe lines 21 and 22 extending to the ends of the cylinder of the fluidactuating motor 20. The latter may be pivotally mounted upon suitablesupporting structure, as by the pivot 23, and is provided with aninternal piston attached to the piston rod 24 pivotally connected to themember to be actuated, such as indicated at 25. 7

Referring now to Fig. 2, the pressurized reservoir assembly 10, havingan internal storage space 19a, has mounted thereon the auxiliarypressurizing cylinder 8 supplied through the pump discharge branch 7.The main body of the reservoir 10 is formed by the cylindrical shell orcasing 26 which has fitted thereto at its upper end the top head element27 suitably apertured for the auxiliary cylinder 8, and the casing 26also has the bottom head element 28 fitted to the bottom thereof. Thecasing head element 27 is provided with an orifice or passage 27a whichserves to vent the space directly beneath the casing head 27 to theatmosphere. The casing bottom 28 is provided with a suitable seal at2311 as well as the fill and drain plug 2 b, and both casing heads 27and 28 may be of hexagonal or other polygonal shape in plan form, beingsuitably apertured to receive the plurality of tie rods or bolts 29 bywhich the end elements 27 and 28 are drawn together by tensioning thebolts 29 for the retention of the casing head on both ends of the casingshell 26.

A main piston element 30 is reciprocably slidable within the internalbore of the casing wall 26, being sealed thereagainst by the O-ring orother seal means 31 and having a transverse diaphragm wall 32. On theunderside of the latter, there is formed, or suitably attached, acentrally disposed pin 33 having a lock collar 33a for the retention onthe pin 33 of the pivotal link element 34. The link member 34 extendsradially from the centrally disposed pin 33 and carries a pivotalconnection 34a at its outer end to the folding linkage 35-36. The links35 and 36 are intermediately pivoted at 35a, both being of substantiallythe same length, and the lower end of thelower link 36 is attached to afurthertransverse .pin 37 suitably journalled in the lower head element28. The pin 37 extends through the outer wall of the head element 28through a suitable liquid-tight seal and has the pointer 33 of theindicating means 15 secured thereto. The pointer 38, as the piston movesdownwardly within the casing bore 26, folding the linkage 3536, isrotated in the clockwise direction from its substantially horizontalfull position to its substantially empty position shown in theconstruction lines in Fig. 2. Suitable graduations may be provided onthe quadrant 39 to provide the scale for the indicator 5 as may be shownby the lever 38 serving as the pointer.

I Within the bore of the auxiliary cylinder 8, there is provided thehollow elongated piston 40 of relatively small diameter as compared withthe diameter of the main piston 39. The end of the bore of the auxiliarycylinder 8 is suitably plugged by the threaded plug tting 41 and theouter surface of the piston 40 is suitably sealed and made fluid-tightwhere it passes through the lower hub portions of the cylinder 3 as bymeans of the Q-ring seal 42. The adjacent hub portion ofthe cylinder 3is provided with a transversely extending flange 43 by means of whichthe casing of the cylinder 8 is secured to the undersurface of the maincasing head 27 as by the attachment bolts 44. The lower end of the smallauxiliary pistion 40 has secured thereto the enlarged diameter flange orplunger portion 45 which is adapted to bear downwardly against thetransverse diaphragm or web 32 of the main piston 39.

When the hydraulic system shown in the drawings, is filled with fluid,care must be taken to insure that the storage space 19a within thereceiver is completely filled with liquid and all air has been expelledfrom beneath the main piston 30. It is also essential that when thesystem is filled all of the lines and the space within the cylinder ofthe actuating motor 20 as well as the cylinder 3 are all completelyfilled with fluid and devoid of air. This may be accomplished in anumber of ways familiar to those skilled in the hydraulics art and maybe done by venting the highest points of the system as well as any otherhigh points in which air might become trapped. As the pump 5 is startedit will be seen that it has ample fluid to insure its being properlyprimed and immediately as the pump delivers fluid under pressure intothe discharge line, this pressure is also transmitted through the branchline 7 and is exerted downwardly upon the exposed cross-sectional areaof the auxiliary piston 46. This downward force, due to the pumpdischarge pressure, is exerted by the plunger 45 upon the main piston 3%which transmits this pressure to the upper surface of the liquid storedwithin the reservoir storage space 10a. The amount of pressurization isdetermined by the ratio of exposed piston areas as well as the cut-outpressure of the system and may be varied to suit any individualinstallation.

Any reduction in volume of the liquid stored within the space 10a, 'aswell as any reduced pressure due to the starting of the pump 5 and thewithdrawal of fluid through the suction line 14, is immediately taken-upand more than compensated for by the increased pressure developed by theauxiliary piston 40 causing the main piston to be moved downwardly andto thereby maintain a pressurized condition within the reservoir 19. Inthe event of leakage from the hydraulic system or loss from excesspressures relieved through the pressure relief valve 17 causingreduction in the volume of the fluid stored within the space ltla, thepiston 3G is automatically forced down upon the reduced volume of theliquid to maintain the desired back pressure or suction head upon thepump 5 to avoid any possibility of cavitation. As the main piston 3i)moves downwardly within the casing 26 of the reservoir 10, air ispermitted to enter through the opening 27a into the space above thepiston 39 and below the casing head 27 so as not to create a suctionwhich might oppose the force exerted upon the auxiliary piston forpressurizing the liquid. Also as the main piston 30 moves 4 downwardlywithin the reservoir the pivotally interconnected links 35 and 36 tendto fold or flatten out indicating their relative position and that ofthe piston 30 on the indicating means 15. The selector control valve 18and the fluid actuator motor 20 have been shown and described by way ofexample only and it will be obvious that the improved anti-cavitationmeans is applicable for use with other hydraulic components than thosewhich have been illustrated, and in hydraulic systems other than the general type which has been shown.

It will be understood that the modification which has been shown anddescribed is by way of example only, that it simply represents one formof the invention and should not in any way be considered as a limitationthereto. For example, reservoir units of the type disclosed have alsobeen very satisfactorily employed when disposed in a normally horizontalposition, such as would be assumed by the unit by rotating Fig. 2 of thedrawings 90 in clockwise direction to the lengthwise position with thepressurizing unit to the right. This permits outlet 16 to be disposed atthe top left to provide a vent for any air which may have entered thefluid chamber 10a, for which purpose the small recessed space adjacentthe outlet 16 within the end member 28 has been provided. In othermodifications of the reservoir units round end heads have been providedin place of the polygonal type which has been shown and described. Otherforms and modifications of the present invention which will occur tothose skilled in the art after reading the foregoing description, areintended to come within the scope and spirit of this invention, as moreparticularly set forth in'the appended claims.

We claimi l. A pressurized reservoir unit for receiving hydraulic fluidfrom and supplying the same to a pump in a cavitanon-free arrangement,comprising a cylindrical casing having an internal bore, a primarypiston slidable within said cylindrical bore defining a reservoirchamber on one side thereof, fluid connections for the supply of fluidto and from said pump to said reservoir chamber, a secondary cylinderformed by said casing, a secondary piston of lesser diameter than saidprimary piston slidably mounted within said secondary cylinder andhaving a portion in engagement with said primary piston, and conduitmeans in communication with the discharge of the pump and the interiorof said secondary cylinder for transmission of fluid pressure to saidsecondary piston whereby a force is exerted by engagement with saidprimary piston for the pressurization of the fluid within said reservoirchamber for the minimization of cavitation in the supply of liquid tothe pump from said pressurized reservoir chamber.

2. A cavitation-free pressurized reservoir for hydraulic fluid supply toa pump comprising a cylindrical casing having an internal bore, endfittings for enclosing the ends of said cylindrical casing, a floatingpiston slidable within said cylindrical bore and defining a reservoirchamber on a first side thereof, fluid connections to said reservoirchamber for the supply of fluid to and from a pump, a secondary cylinderof smaller diameter than said internal bore supported from said casing,a piston slidably mounted within said secondary cylinder having aportion in engagement with said floating piston, conduit means incommunication with the interior of said secondary cylinder fortransmission of fluid pressure from the pump to said secondary pistonfor the exertion of a force against said floating piston for thepressurization of the fluid within said reservoir chamber for thecavitation-free supply to the pump.

3. A pressurized reservoir unit for receiving hydraulic fluid from andsupplying it to a pump in a cavitation-free arrangement, comprising acylindrical casing having an internal bore, end fittings for enclosingthe ends of said cylindrical casing, a free piston slidable within saidcylindrical bore dividing said bore into a chamber open to theatmosphere on a first side of said free piston and a reservoir chamberon the second side of said free picton, fluid connections for the supplyof fluid to and from said pump to said reservoir chamber within saidcylindrical casing on said second side of said floating piston, asecondary cylinder of smaller diameter than said internal bore supportedfrom said casing, a secondary piston slidably mounted within saidsecondary cylinder having a portion in engagement with said free piston,and conduit means in communication with the discharge of the pump andthe interior of said secondary cylinder for transmission of fluidpressure to said secondary piston whereby a force is exerted by it bydirect engagement against said free piston on its atmospheric chamberside for the pres surization of the fluid within said reservoir chamberfor the minimization of cavitation in the supply of liquid to the pumpfrom said pressurized reservoir chamber.

4. In a pressurized reservoir system, a fixed casing having acylindrical chamber therein forming a reservoir for the supply ofhydraulic fluid to the suction inlet of a pump, a primary pistonreciprocable within said fixed c'as ing dividing the same into anunpressun'zed chamber and a reservoir chamber for fluid under pressure,a secondary cylindrical chamber formed adjacent said unpressurizedchamber by an intermediate transverse wall extending across said casing,said transverse wall having a central aperture, said secondary chambercommunicating with the discharge outlet of the pump to receive highpressure hydraulic fluid therefrom, a secondary piston reciprocableWithin said aperture through said transverse Wall and having a portiondisposed within said high pressure secondary chamber subjected to saidfluid discharge pressure, said secondary piston being in engagement withsaid primary piston whereby both said pistons move together under theinfluence of the respective pressures within said high pressure chamberand said reservoir chamber and a fluid pressure of suflicient magnitudeis maintained within said reservoir chamber for preventing cavitation inthe fluid supply to the suction inlet of the pump.

References Cited in the file of this patent UNITED STATES PATENTS2,349,253 Edmond May 23, 1944 2,426,320 Messinger Aug. 26, 19472,440,065 Ashton Apr. 20, 1948 2,605,716 Huber Aug. 5, 1952 2,673,527Ashton et a1 Mar. 30, 1954

